A conventional microwave oven cooks food by a process of dielectric heating in which a high-frequency alternating electromagnetic field is distributed throughout an enclosed cavity. A sub-band of the radio frequency spectrum, microwave frequencies at or around 2.45 GHz, cause dielectric heating primarily by absorption of energy in water.
To generate microwave frequency radiation in a conventional microwave, a voltage applied to a high-voltage transformer results in a high-voltage power that is applied to a magnetron that generates microwave frequency radiation. The microwaves are then transmitted to the enclosed cavity containing the food through a waveguide. Standards, such as set by the Food and Drug Administration (FDA), limit the amount of microwave radiation that can leak from an oven throughout its lifetime. Consequently, the door of a microwave oven must limit the transmission of microwave radiation from the enclosed cavity to the surrounding environment. The standard also requires microwave ovens to have two independent interlock systems that stop the production of microwaves the moment the door is opened. Additionally, the door must be aesthetically pleasing and provide a viewing window to permit the visual inspection of the enclosed cavity and the food contained therein. Typically, a perforated metallic shield disposed in or adjacent to a viewing window bars the transmission of microwave radiation through the window.